This invention relates to an improved machine for mass producing locking patches of thermoplastic material on circumferentially and axially limited threaded portions of magnetic elements, such as screws, of the type disclosed in Barnes U.S. Pat. No. 3,831,736.
Barnes U.S. Pat. No. 3,831,736 also discloses a machine for mass producing locking patches on magnetic screws, in which machine such screws are placed on closely spaced magnetic fixtures mounted on an endless belt which carries the screws in succession, with the screw axes horizontal, past a heating station and thence past a powder applying station where the heated screws pass through a freely falling stream of powder of the thermoplastic material. The powder melts upon striking the heated screws and on cooling solidifies, to produce patches bonded to the screw threads. The machine disclosed in the aforesaid Barnes patent is subject to the disadvantage that it is quite difficult, time-consuming and expensive to change-over from patching one type of screw to another, in that the entire belt must be replaced.
Burke et al. U.S. Pat. No. 3,452,714 discloses apparatus for producing locking patches on headed screws, in which the screws are transported with their axes vertical, suspended by their heads between two parallel belts. Thus suspended, the screws are transported past a heating station and a powder applying station where powder is blown in a horizontal stream against the threads of the heated screws. The machine disclosed in the aforesaid Burke et al. patent is subject to the disadvantage that it is incapable of handling headless screws, such as set screws.
Burke U.S. Pat. No. 3,530,827 discloses a so-called "pinwheel" machine for patching headless screws such as set screws, but the output of the machine is limited by the fact that the screws must be hand fed to the machine.
There is also a prior art machine for producing locking patches on magnetic screws, this machine comprising a magnetic dial which is of one-piece monolithic construction. As in the machine of the present invention, the screws are held magnetically on the periphery of the dial which is rotated about its axis to carry the screws past a heating station and a powder applying station. However, it has been found in the operation of that prior art magnetic dial machine that if the dial is rotated with sufficient speed to achieve economical production rates, the capacity of the heater must be so great that excessive heat builds up in the dial itself, with the result that the dial loses its magnetisim and the main bearings of the machine very quickly become ruined, necessitating that the machine be shut down and rebuilt.
It is therefore an important object of the present invention to provide an improved magnetic dial machine which overcomes the aforementioned disadvantages of the prior art and particularly wherein heat dissipation is provided for, to make possible higher speed operation for long periods of time.
It is another important object of the present invention to provide a magnetic dial machine wherein, in the event of damage to or deterioration of a section of the dial assembly, ready replacement of the damaged dial section is possible.